1. Technical Field
The invention relates to a method for the detection of objects in a detection region in which at least one transmitted light bundle is transmitted into the detection region and transmitted light reflected back or remitted back by an object is detected, when present, by a receiver unit, with the distance of the object being determined by triangulation from the position of the at least one light patch generated by the light reflected or remitted at the receiver unit. The invention furthermore relates to an optical sensor for the carrying out of the method in accordance with the invention.
2. Description of Related Art
It is known to determine the distance of real objects in a detection region, for example, in optical sensors using the so-called triangulation principle. For this purpose, the sensor comprises a transmission unit, for example, a light emitting diode or a laser unit having a corresponding optical transmission system, said sensor transmitting a light beam into the detection region to an object to be detected, when present there. The light reflected or remitted by such an object is detected by a receiver which comprises a receiver unit and an optical receiver system which directs the reflected or remitted light to the receiver unit. The receiver unit comprises an array of photosensitive elements in known solutions. Both the transmitter and the receiver as a rule include a corresponding optical transmission or reception system which are arranged next to one another (so called “double-eye system”). The position of the detected light on the detector changes in dependence on the distance between the sensor and the reflecting object. There is a clear geometrical relationship between the point of incidence on the detector and the distance of the detected object. An evaluation of the light distribution on the receiver array, as a rule by evaluation of the location of the center of intensity of the light patch, can therefore be used for the distance determination. Such a triangulation sensor is described, for example, in DE 197 21 105 A1.
DE 102 38 075 B4 describes a triangulation sensor having two parallel measurement channels which are formed in that two lasers transmit light in parallel into the detection region, said light being detected by two correspondingly arranged arrays of light-sensitive elements.
The above-described known triangulation process can be error-prone or bring along an imprecise scanning distance estimate under certain circumstances, in particular if the object is shiny, that is it is not of a “Lambertian” remission characteristic, or if the transmitted light bundle simultaneously detects a plurality of objects at different distances in the detection range. In addition, it can be problematic if the transmitted light bundle is defected by shiny metallic surfaces on the way to or from the object to be detected or if reflective surfaces are present in the background. Objects moving in the detection region can also be problematic, in particular if the object moves from the deep in the direction of the transmitter/receiver arrangement. Finally, it can be problematic if an object has different remission or reflection properties at different surface regions. This namely has the result that the energetic center of intensity of the reflected light deviates from the geometrical center of intensity so that the center of intensity evaluation becomes imprecise at the array of light-sensitive elements.
It is known for light barriers to transmit light through a monitored zone onto a stationary two-dimensional reflector or retroreflector. The reflected light is reflected back to a receiver again through the monitored zone. An object which is located in the monitored zone blocks the light path so that a corresponding signal can be generated. It is known from DE 10 2005 060 399 A1 for light barriers to use two-dimensional receiver arrays to be able to detect deviations from a light patch geometry which is expected when there is no object in the monitored zone.
Other systems work in accordance with the camera principle in which an image of a scene is taken and is supplied completely to an evaluation unit. Specific features, for example object shape, object location or object movement, are then analyzed and evaluated with the help of corresponding image processing algorithms to obtain information on the object located in the detection region.
DE 10 2005 062 258 A1 describes a triangulation sensor in which a distance determination in accordance with the triangulation principle is carried out. For this purpose, a multi-reception element is used on whose operation the breadth of the signal curves of the reception light patches on the multi-reception element is determined. Differently shiny objects can thus be detected reliably and optionally a printing or structuring of the object surface can be evaluated.
DE 10 2004 053 219 B3 describes an optical sensor in which the energy distribution of a light patch is evaluated at a receiver unit by column-wise or row-wise summation of the output signals.
A method for the detection of objects in a detection region having the features of the preamble of claim 1 is known from DE 10 2007 003 024 A1.